tokio_dual_stack

tokio_dual_stack is a library that adds a "dual-stack" TcpListener.

Why is this useful?

Only certain platforms offer the ability for one socket to handle both IPv6 and IPv4 requests (e.g., OpenBSD does not). For the platforms that do, it is often dependent on runtime configuration (e.g., IPV6_V6ONLY). Additionally those platforms that support it often require the "wildcard" IPv6 address to be used (i.e., ::) which has the unfortunate consequence of preventing other services from using the same protocol port.

There are a few ways to work around this issue. One is to deploy the same service twice: one that uses an IPv6 socket and the other that uses an IPv4 socket. This can complicate deployments (e.g., the application may not have been written with the expectation that multiple deployments could be running at the same time) in addition to using more resources. Another is for the application to manually handle each socket (e.g., select/join each TcpListener::accept).

DualStackTcpListener chooses an implementation similar to what the equivalent select would do while also ensuring that one socket does not "starve" another by ensuring each socket is fairly given an opportunity to TcpListener::accept a connection. This has the nice benefit of having a similar API to what a single TcpListener would have as well as having similar performance to a socket that does handle both IPv6 and IPv4 requests.

Minimum Supported Rust Version (MSRV)

This will frequently be updated to be the same as stable. Specifically, any time stable is updated and that update has "useful" features or compilation no longer succeeds (e.g., due to new compiler lints), then MSRV will be updated.

MSRV changes will correspond to a SemVer patch version bump pre-1.0.0; otherwise a minor version bump.

SemVer Policy

• All on-by-default features of this library are covered by SemVer
• MSRV is considered exempt from SemVer as noted above

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE)
• MIT license (LICENSE-MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Before any PR is sent, cargo clippy and cargo t should be run. Additionally RUSTDOCFLAGS="--cfg docsrs" cargo +nightly doc --all-features should be run to ensure documentation can be built.

Status

This package is actively maintained and will conform to the latest version of tokio.

The crate is only tested on x86_64-unknown-linux-gnu and x86_64-unknown-openbsd targets, but it should work on most platforms.